Optical transmission technology has a development trend toward higher single-channel speed (e.g., single-channel 400 G/1 T transmission), higher spectral efficiency, and high order modulation formats. Thus, the most clear and important direction in the development of optical transmission is still to further increase the speed. High-speed transmission faces many restrictions, mainly in two aspects: on one aspect, the optical transmission technology evolves to high spectral efficiency aggregation transmission and high speed service interface transmission, so that if the spectral efficiency cannot be further improved, it makes little sense to perform low-speed aggregation and then high-speed transmission, however, since there may be still Ethernet interfaces on the client sides, the problem of high-speed interface transmission will still be considered, and 400 G will be a critical point of the spectral efficiency limit; on the other aspect, the optical transmission technology evolves to long distance (long cross segment and multi-cross segment), so that although the Optical Signal Noise Ratio (OSNR) of system can be improved by technical means, such as using low-loss optical fiber and low-noise amplifier and reducing cross segment distance, the improvements caused by these technical means are too limited to make a significant breakthrough, and it is also difficult to implement in engineering.
With the growing requirement on the bandwidth of bearer network, the technology beyond 100G is a solution for satisfying the requirement of bandwidth increases. However, for the transmission bandwidth beyond 100G, whether it is 400G or 1T, the traditional 50 GHz Fixed Grid Wavelength Division Multiplexing (WDM) cannot provide enough spectral width to realize the technology beyond 100G. On account of the defect of fixed grid, it is required to propose wider Flexible Grid.
In the related arts, the requirements on channel width are different due to the multi-speed mixed transmission beyond 100 G and the flexibility of modulation format beyond 100 G, and if each channel is customized with an appropriate bandwidth, the system bandwidth can be utilized sufficiently, so that a flexible grid system is generated. Based on the requirement on high-speed WDM system due to the growing increases of bandwidth requirement, it is required to introduce Flexible Grid technology. However, there are many problems to be solved, e.g., how to effectively perform frequency spectrum planning and management, and the compatibility with existing systems.
G698.x defines a Black Link Standard to define characteristics of optical layers of single optical channel between an optical transmitter and an optical domain and between the optical domain and a receiver. The G698.x standard defines physical signal features and application codes of S (sending) reference points and R (receiving) reference points. The application code defines the modulation format and FEC (Forward Error Correction) of a transmitter or receiver. Interfaces corresponding to the S reference points and R reference points defined by G698.x are not defined in G709, and there is no Optical Transport Network (OTN) interfaces which are compatible with the S reference points and R reference points, and more importantly, there is no independent Optical Supervisory Channel (OSC) between the transmitter and the optical domain and between the optical domain and the receiver. Thus, out-of-band optical channel overhead cannot be provided for the optical channel between the transmitter and the optical domain and between the optical domain and the receiver. However, inside the optical domain, the optical supervisory channel can be used to carry optical channel overhead and optical multiplex section overhead and optical regeneration section overhead to provide the optical network management capability. The optical channel overhead (OCh-Overhead) is generally carried in an OSC, wherein the OSC, an optical channel payload (OCh-Payload), the optical multiplex section and the optical regeneration section are transported in the same optical fiber. However, there is no specification in the G709 standard to specify a Protocol Data Unit (PDU) format carrying the optical channel overhead at present.
The transmitter of the current customer interface uses a tunable laser, and a tunable optical receiver will be used in the future, that is, the transmitter and the receiver may dynamically adjust central frequency according to a configured Nominal Central Frequency (NCF) and an application code (e.g., modulation format, and FEC) to transmit or receive optical signals. For the extra flexibility, it is required to negotiate a single, unified NCF and application code between the optical receiver and the optical transmitter, so that the optical signals can be correctly sent and received. Meanwhile, it is also required to negotiate a unified NCF and an application code between two ends of the S (sending) reference points and R (receiving) reference points, so that the optical domain may flexibly configure the receiver and transmitter according to the negotiated NCF and the negotiated application code.
However, for the problem of how to implement the negotiated unified NCF and the negotiated application code, no effective solution has been proposed in the related art, thus the optical signal could hardly be correctly sent and received.
Aiming at the above-mentioned problem, no effective solution has been proposed.